Cellular mobile communication has evolved from the Universal Mobile Telecommunication System (UMTS) to the Long Term Evolution (LTE). The LTE uses an Orthogonal Frequency Division Multiplexing (OFDM) based scheme as a wireless access technology. The LTE enables high-speed wireless packet communication at peak data rates of 100 Mbps or more in the downlink (DL) and 50 Mbps or more in the uplink (UL).
The 3rd Generation Partnership Project (3GPP), an international standardization organization, has started examining an LTE-based mobile communication system, LTE-Advanced (LTE-A), to implement even higher speed communication. The LTE-A targets high peak data rates of 1 Gbps in the downlink and 500 Mbps in the uplink, and various new techniques including wireless access schemes and network architectures have currently been studied.
For the LTE-A, two scheduling schemes have been proposed: dynamic scheduling and Semi-Persistent Scheduling (SPS). In dynamic scheduling, radio resource allocation for the uplink and for the downlink is signaled through the Physical Downlink Control Channel (PDCCH). In SPS, a base station informs in advance a wireless terminal of communication periodicity in a radio resource control (RRC) connection on Layer 3 (L3). Then, when actual SPS communication is performed, the base station transmits an activation command to the wireless terminal through the PDCCH. The SPS activation command includes information indicating which radio resources are to be continuously used (see, for example, 3GPP TS 36.321, “Medium Access Control (MAC) protocol specification”, V10.1.0, Release 10, March 2011; and 3GPP TS 36.213, “Physical layer procedures”, V10.1.0, Release 10, March 2011).
SPS is used in real-time communication represented, for example, by Voice over Internet Protocol (VoIP). Assume for example that, in a VoIP service, data is sent at 20-ms intervals. In this case, in SPS, the base station informs the wireless terminal of a communication periodicity of 20 ms when an RRC connection is established. Then, when starting SPS communication, the base station transmits an activation command through the PDCCH to thereby inform the wireless terminal of radio resources to be used for the SPS communication.
Thus, in SPS, the base station informs in advance the wireless terminal of the communication periodicity and, then, specifies radio resources allocated for the communication using the PDCCH at the start of the communication. With this, SPS avoids the need to transmit downlink assignments and uplink grants through the PDCCH in the following periodic communication. That is, SPS enables data packets of small size to be transmitted over the Physical Downlink Shared Channel (PDSCH), thus reducing the signaling overhead of the PDCCH.
However, SPS allows only one periodicity to be configured, thus being unable to control more than one communication service.